Bases or base precursors are frequently incorporated into heat developable light-sensitive materials for the purpose of accelerating development upon heating. In view of shelf life of the light-sensitive materials, it is preferred to employ base precursors which release basic substances upon heat decomposition.
Examples of typical base precursors are described in British Pat. No. 998,949. One such base precursor is a salt of a carboxylic acid and an organic base, in which examples of suitable carboxylic acids include trichloroacetic acid and trifluoroacetic acid and examples of suitable bases include guanidine, piperidine, morpholine, p-toluidine and 2-picoline.
Guanidine trichloroacetate is described as a base precursor in U.S. Pat. No. 3,220,846, and aldonic amides as described in Japanese Patent Application (OPI) No. 22625/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") are described as decomposing at a high temperature to form bases.
When these known base precursors are employed in a heat developable light-sensitive material, however, the following problems are often encountered. Specifically, a relatively long development time is required for obtaining images and a high level of fog is formed. Further, they have the disadvantage that the base precursors are susceptible to air and humidity and decompose, changing the photographic properties of the light-sensitive materials and seriously reducing the shelf life of the light-sensitive materials.